The present invention relates to an ink-jet printer, which emits ink particles onto a recording medium to prints an image on the recording medium, and specifically relates to an ink-jet printer, in which moving velocities of the ink particles, being micro droplets of ink, are detected to perform stable emitting actions of the ink particles.
In recent years, a great number of image printing methods using an ink-jet printer have been employed as convenient methods for forming images at a reduced cost. The ink-jet printer prints images onto paper or other recording media by emitting ink as ink particles from a plurality of emission ports towards the recording media by use of a voltage applied to a piezoelectric element or heater provided on the ink-jetting head of the printer, and then scanning the recording media with the ink-jetting head while fixing the ink onto the recording media.
However, to print images on recording media with stable accuracy, ink particles emitted from the emission ports of each nozzle are required to hit the recording media at properly timed intervals according to the particular operation of the ink-jetting head. It is preferable, therefore, that the emission velocity of ink from each nozzle of the ink-jetting head should be kept constant.
According to the prior art practice, however, the velocity of ink particles emitted may vary according to each emission port if the status of the emission ports deteriorates due to drying of the ink or the ingress of dirt, air bubbles or the like.
Further, a plurality of ink-jetting heads are used to implement color printing according to the prior art. In this case, however, the velocity of the ink particles emitted may also differ depending on the ink-jetting heads because of idiosyncrasies of each recording head and the type of ink used in each ink-jetting head.
If the velocity of the ink particles emitted differs depending on according to each emission port of the ink-jetting head or each ink-jetting head, image-printing accuracy may deteriorated, as described above.
For example, if the emission velocity of ink particles changes at some emission ports, the status of the emission ports may have been deteriorated, as described above. If this trouble is left unprepared, ink may not be emitted from some of the nozzles.
Further, the ink-jet recorder emits ink particles in the form of minute liquid droplets from a multitude of nozzles formed on the ink-jetting head so that they will hit the recording media arranged so as to face the nozzle surfaces of the ink-jetting head. Then a desired image is recorded and formed on the recording media during main scanning of the ink-jetting head in both directions.
To achieve high-quality image recording with such an ink-jet recorder, it is necessary to keep track of how the ink particles are emitted from each nozzle of the ink-jetting head. If the ink particles emitted from each nozzle of the ink-jetting head are kept in a constant status, there will be deviations in the position of ink particles reaching the recording media during main scanning of the recording media in both directions by the ink-jetting head. For example, if the velocity of ink particles emitted from each nozzle of the ink-jetting head is lower than the intended velocity, the ink particle “a” that should hit a target line X on the recording media reaches a position deviated from the target line X by the distance corresponding to the lower velocity, as shown in FIG. 18. This is repeated for each main-scanning operation of the ink-jetting head in both directions (indicated by the arrow). Deviations in the position hit by ink particles in both directions will cause disturbances in the image recorded, thus reducing resolution significantly.
Since changes in the velocity of ink particles appear as changes in the amount of particles, the density of the recorded image will change, and the color balance of the image will also be changed.
Further, when the stable driving conditions for ink particle emission of the ink-jetting head are not met, air will be entrapped into the ink chamber to prevent ink particles from being emitted correctly, or ink particles will take a curved course, resulting in stripe-like irregularities. This will cause image quality to deteriorate significantly.
When the ink-jetting head consists of a plurality of ink-jetting heads that records images using ink of different colors such as yellow (Y), magenta (M), cyan (C), and black (K), the position hit by ink particles varies from color to color due to the difference in the distance between the recording medium of each ink-jetting head and the head surface.
The prior art of detecting the velocities of the minute ink particles emitted from the ink-jetting head, and modifying and controlling the ink-jetting head driving conditions based on the detection is disclosed in the Official Gazette of Japanese Application Patent Laid-Open Publication No. Hei 11-300944. According to this prior art, however, the velocities of the particles emitted from the multiple nozzles formed on the ink-jetting heads are detected for each nozzle. To detect the velocities of the particles emitted from all nozzles, more time is required. Namely, each ink-jetting head must be stopped to ensure that ink particles emitted from each nozzle of the ink-jetting head will match the detection position (an optical path of detecting beam or detecting range) of velocity detection means. This requires a very high positioning accuracy when the ink-jetting head is positioned at the detection position. Thus, a lot of time must be consumed in the control of stop position, hence velocity detection, according to the aforementioned prior art. Especially when the recording mechanism has a plurality of ink-jetting heads for ink of different colors, a great deal of time is required since each ink-jetting head must be stopped to detect velocities.